docs: Update outdated documentation to reflect current application state

[Copilot]

The documentation in the docs/ folder was significantly outdated and did not reflect the current state of the Mergington High School Management System. This PR comprehensively updates all documentation to accurately represent the application's features, API endpoints, and architecture.

Key Updates Made

API Documentation

• Added AuthController endpoints: Documented the complete /auth API including login and session management
• Enhanced Activities API: Updated with accurate request/response examples, proper HTTP status codes, and comprehensive parameter documentation
• Added missing endpoints: Documented StaticController for frontend serving and health check endpoints

Architecture & Code Structure

• Updated package structure: Fixed discrepancies between documented and actual file organization
• Added new DTOs: Documented ActivityTypeDTO, LoginRequestDTO, and enhanced ActivityDTO structure
• Enhanced Value Objects: Added documentation for ActivityType enum with automatic categorization system

Frontend Features

• Categorization System: Documented the 5-category activity system (Sports, Arts, Academic, Community, Technology) with visual color coding
• Filter System: Added documentation for dynamic filtering by category, day, and time
• Authentication UI: Documented the modal-based login system and session management

Configuration & Environment

• Environment Variables: Updated with actual variables from .env.example including teacher passwords for database seeding
• Development Profile: Added details about CORS configuration, logging levels, and DevTools setup
• Database Seeding: Documented current 14 activities and 4 seeded teachers with proper credentials

Data Structures

Added comprehensive documentation for all DTOs and Value Objects:

// Example: ActivityDTO with complete structure
public record ActivityDTO(
    String name,
    String description, 
    String schedule,
    ScheduleDetailsDTO scheduleDetails,
    int maxParticipants,
    List<String> participants,
    int currentParticipantCount,
    ActivityTypeDTO type  // New: category with visual information
)

Verification

• ✅ Tested all documented API endpoints against running application
• ✅ Verified frontend functionality matches documentation
• ✅ Confirmed environment variables and configuration examples work
• ✅ Validated database seeding produces documented sample data

The documentation now provides an accurate, comprehensive guide to the current application state with no outdated information.

Fixes #7.

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